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STUDIA UNIVERSITATIS BABEŞ-BOLYAI, GEOLOGIA, XLVIII, 1, 2003, 77-84
SERPIERITE Ca(Cu,Zn)4(OH)6(SO4)2·3H2O - THE FIRST
OCCURENCE IN ROMANIA
LUMINIŢA ZAHARIA1
ABSTRACT. Serpierite Ca(Cu,Zn)4(OH)6(SO4)2·3H2O occurs as small blue crusts
covering millimeter-size gypsum crystals on the ceiling of a small mining gallery in
Trestia-Băiţa area, Metaliferi Mountains. X-ray diffraction, optical, and scanning electron
microscope with EDX and Raman spectroscopy have been used to identify the mineral.
Genetically, serpierite derived from weathering of primary hydrothermal cooper and
lead deposits. This is the first reported occurrence of serpierite in Romania.
Keywords: Serpierite, hydrothermal, Trestia-Băiţa, Metaliferi Mountains, Romania.
INTRODUCTION
Serpierite is a hydrated copper calcium sulfate first described in the mines
of Laurion (Greece) by Bertrand (1881) (in Sabelli & Zanazzi, 1968). Its first
description, including optical properties and crystal morphology, was given by Des
Cloizeaux (1881) (in Sabelli & Zanazzi, 1968). Faraone et al. (1967) determined
the cell parameters and space group, showing that the mineral belongs to the
monoclinic system. They carried out investigation on chemical properties, which
leads them to the formula of the serpierite. The crystal analysis of the mineral,
presenting its structural features was made by Sabelli & Zanazzi (1968).
In Romania, serpierite has been found in a mining gallery that intersects
the Cave No. 4 from Runcului Hill. The cave is located in the southeastern part
of Trestia-Băiţa metalogenic district, Metaliferi Mountains (Romania), at 455 asl. It
is the largest cave in the respective karst area and consists of several rooms
linked by small pits and narrow passages. The mining gallery, which is no
longer connected to the surface, was discovered during the exploration of the
cave and was probably dug for prospecting a hydrothermal vein. Serpierite was
found as small blue crusts on tiny gypsum crystals on the ceiling, within the
hydrothermal vein excavation (Fig.1).
GEOLOGICAL SETTING
The basement in the cave area consists of Early Jurassic ophiolites,
represented by pyroclastic basalts, covered by Tithonic-Berriasian limestone blocks.
Both ophiolites and limestones are part of the Căpâlnaş-Techereu Nappe (Balintoni,
1997). Starting with the Sarmatian, quartiferous amphibolitic andesites (known
as Barza Andesites) were placed in the entire area as lava flows and intrusive
bodies (Bordea & Borcoş, 1972) (Fig. 2). The hydrothermal activity associated
to the Neogene volcanism (2nd Cycle) resulted in the formation of several sulfide
veins, emplaced both within limestones and basalts (Ianovici et al., 1969).
1 "Babeş-Bolyai" University, Department of Mineralogy, 1, Kogălniceanu str., 3400 Cluj-Napoca, Romania
LUMINIŢA ZAHARIA
78
Fig. 1. The location of Cave No. 4 in Romania and the sampling point of serpierite.
Fig. 2. Geological map of the investigated area (after Bordea & Borcoş, 1972).
1,9 Miocene sedimentary complexes; 2,5,8 Barza Andesites;
3,7 Ophiolites; 4 Reefal limestone; 6 Băiţa Dacites.
SERPIERITE Ca(Cu,Zn)4(OH)6(SO4)2·3H2O - THE FIRST OCCURENCE IN ROMANIA
79
ANALYTICAL METHODS
X-ray diffraction analysis
The X-ray powder diffraction obtained on a Phillips diffractometer (Cu-Kα,
λα1 = 1.54060) was used for the identification of the mineral. The lines of the
pattern are well marked and sharp (Fig 3). The cell parameters obtained by least-
squares refinement of XRD data, using the UnitCell Program (Holland & Redfern,
1997) are given in Table 1. The refinement was carried out using 18 powder
reflections in the 2θ range 5 -70o, with a step interval of 0.01o 2θ. As shown in
Table 1, the cell parameters of the Runcului Hill serpierite have close values
with the ones reported in ICDD catalog.
Table 1.
Comparison of cell parameters for serpierite from Runcului and ICDD catalog.
Serpierite from Runcului Hill ICDD 22-148
a = 22.1935
b = 6.2431
c = 21.8480
β =113.252
a = 22.186
b = 6.250
c = 21.853
β= 113.37
Fig. 3. The diffraction pattern of serpierite.
Optical and scanning electron microscope analyses
A Nikon Optiphot 2-POL binocular at 50x magnification was used to
observe serpierite habitus. The observations revealed that thin sky-blue crusts
coat millimeter-size, transparent to translucent, colorless gypsum crystals.
Minor amounts of clay may occur on top of gypsum, together with serpierite.
LUMINIŢA ZAHARIA
80
The SEM investigations were conducted on a Jeol Scanning Electron
Microscope. They revealed lamellar to tabular crystals, scattered or packed as
the pages of a book (Plate I, Fig. 1 & 2). Four crystals of serpierite were examined
by means of electron microanalysis, using an EDX detector attached to the
SEM. The semi-quantitative elemental analysis accounts the participation of Ca
(5.906 %), Cu (31.5 %), Zn (11.39 %), S (9.086 %) and O (42.118 %). Copper
shows the highest concentration of all the metallic ions.
Raman spectroscopy analysis
The Raman spectrum recorded from the almost pure serpierite sample
was in the measured range of 0-3700 cm-1. The wave number, characters and
intensities of the bands are reported in Table 2, while the spectrum between 0-
1300 cm-1 is presented in the Fig. 4. As the Raman spectrum deals mostly with
IR one, for the same mineral, the interpretation of the peak position was made
according with Farmer (1974).
The spectrum shows two distinctive absorption bands in the region of
the O-H stretching vibration. These are characteristic for the hydrogen-bound O-H
stretching and correspond to the weakly bounded OH or to molecular water.
The vibrational bands at 1133, 1074, 987, 646, 609, 482 and 445 cm-1
may be assigned to the vibrational modes of the SO4 structural group.
Table 2.
Position and assumptions concerning the Raman bands recorded for the
serpierite from Runcului Hill.
Raman shift (cm-1) Structural group Vibrational mode Intensity, character1
3611 (OH)-, H2O O-H stretching m, br
3558 (OH)-, H2O O-H stretching m, br
1133 SO4 antisymmetric stretching s, sh
1074 SO4 antisymmetric stretching m, sh
987 SO4 symmetric stretching vs, sh
646 SO4 antisymmetric bending w, sh
609 SO4 antisymmetric bending m, sh
482 SO4 symmetric bending m, br
445 SO4 symmetric bending s, sh
332, 252 - lattice modes w, br
1 s=strong; m=medium; w=weak; vs= very strong; sh=sharp; b=broad;
SERPIERITE Ca(Cu,Zn)4(OH)6(SO4)2·3H2O - THE FIRST OCCURENCE IN ROMANIA
81
Fig. 4. Raman spectrum of serpierite.
DISCUSSION AND CONCLUSION
The Cave no 4 from Runcului Hill has a vadose origin, but some
features indicating hydrothermal influences were recognized. These are the
close vicinity with the hydrothermal veins and „exotic” hydrothermally-deposited
minerals (barite, galena, cerusite, quartz) occurring in the cave (Zaharia et al.,
unpubl. data). The degree of hydrothermal influence is difficult to establish due
to the thick clay layer covering the floor, and the walls and ceiling of the cave at
several locations which did not allow a good observation of the morphology.
The excavated part has a high grade of alteration, resulted in the earth masses
and crusts occurring on the walls.
All the analyses implied confirm the presence of serpierite. Macroscopically
it looks like sky-blue crusts, coating gypsum crystals, whereas microscopically,
under SEM, serpierite shows thin elongated plates, scattered or packed. Both
the X-ray diffraction and Raman spectral analyse showed an almost pure
sample.
Serpierite is associated with gypsum. We assume that the crystallization
sequence starts with precipitation of gypsum. The Ca-depleted solution suffered a
change of the relative Cu:Zn:Ca ratio, which allowed a precipitation of serpierite.
Primary metallic mineral formed within the hydrothermal vein, provide the ions
of copper and zinc.
Acknowledgements. We wish to thank Professors Herta Effenberger
and Eugen Libowitzky for their invaluable help during the analytical stage. We
are also indebted to Tudor Tamaş for his assistance during the fieldwork and his
comments on an earlier draft of this manuscript. The analyses were performed at
LUMINIŢA ZAHARIA
82
the Institute of Mineralogy and Crystallography, University of Vienna, by the author,
during a research scholarship, provided by Prof. Corina Ionescu through the
World Bank Grant 9.
REFERENCES
Balintoni, I. 1997, Geologia terenurilor metamorfice din România. Ed. Carpatica, Cluj-
Napoca, 174 pp.
Bordea, S. & Borcoş, M. 1972, The Geological Map of Romania, 1:50.000, 73d, Brad
sheet.
Faraone, D., Sabelli, C. & Zanazzi, P. F. 1967, Su di solfatibasici idrati : serpierite e
devillite. Atti della Accademia Nazionale dei Lincei. Classe di Scienze Fisiche,
Matematiche e Naturali 43, pp. 369-382.
Farmer, V. C. 1974, The Infrared Spectra of Minerals, Mineralogical Society, London,
534 pp.
Holland, T. J .B. & Redfern, S. A.T. 1997, Unit cell refinement: from powder diffraction data:
the use of regression diagnostics. Mineralogical Magazine 61, pp. 65-77.
Ianovici, V., Giuşcă, D., Ghiţulescu, T. P., Borcoş, M., Lupu, M., Bleahu, M. & Savu, H. 1969,
Evoluţia geologică a Munţilor Metaliferi. Editura Academiei RSR, Bucureşti, 741 pp.
Sabelli, C. & Zanazzi, P. F. 1968, The Crystal Structure of Serpierite, Acta Crystalographica
24, pp. 1214-1221.
SERPIERITE Ca(Cu,Zn)4(OH)6(SO4)2·3H2O - THE FIRST OCCURENCE IN ROMANIA
83
Plate I
Fig. 1. Scattered serpierite crystals (SEM image).
Fig. 2. Packed serpierite crystals (SEM image).
